YTD-1 giving error

I've created a variable for which YTD (CurrentYearToDate) values comes correctly with below formula :

=FormatDate(ToDate(UserResponse([YTD] ; "Date DD/MM/YYYY ?"); "dd/MM/yyyy");"dd-MM-yyyy")

But if I happen to create YTD-1 (PreviousYearSamePeriod) ,Bi4 is giving error. Below is formula used :

=FormatDate(ToDate(UserResponse([YTD -1] ; "Date DD/MM/YYYY ?"); "yyyy-1");"dd-MM-yyyy-1")

Thanks in advance for your help

~S